Credo in unum Deum, Patrem omnipotentem, factórem cæli et terræ, visibílium ómnium et invisibílium. Et in unum Dóminum Iesum Christum, Fílium Dei unigénitum, et ex Patre natum ante ómnia sǽcula: Deum de Deo, lumen de Lúmine, Deum verum de Deo vero, génitum, non factum, consubstantiálem Patri: per quem ómnia facta sunt; qui propter nos hómines et propter nostram salutem, descendit de cælis. Et incarnátus est de Spíritu Sancto ex Maria Vírgine, et homo factus est. Crucifíxus etiam pro nobis sub Póntio Pilato; passus et sepúltus est, et resurrexít tértia die, secundum Scriptúras, et ascéndit in cælum, sedet ad déxteram Patris. Et íterum ventúrus est cum glória, iudicáre vivos et mórtuos, cuius regni non erit fínis. Et in Spíritum Sanctum, Dóminum et vivificántem: qui ex Patre Filioque procédít. Qui cum Patre et Fílio simul adorátur et conglorificátur: qui locútus est per prophétas. Et unam, sanctam, catholicam et apostólicam Ecclésiam. Confíteor unum baptísma in remíssionem peccatórum. Et exspécto resurrectiónem mórtuorum, et vitam ventúri sæculi. Amen.

The First Council of Nicæa, held in 325 on the occasion of the heresy of Arius […]. As early as 320 or 321 St. Alexander, Bishop of Alexandria, convoked a council at Alexandria at which more than one hundred bishops anathematized Arius. The latter continued to officiate and recruit followers, moving to Palestine and Nicomedia. […] Constantine, as sole emperor, sought religious peace. He addressed letters to Alexander and Arius, advising agreement; Hosius of Cordova bore the letter but failed. Seeing this, Constantine […] judged an œcumenical council necessary.

The emperor invited bishops from all countries, including Persia. It is not known whether he acted solely or with the pope […]. Nicaea was favourable for bishops from Asia, Syria, Palestine, Egypt, Greece, and Thrace. Sessions were held in the principal church and imperial palace. A large place was necessary, though […] the exact number is unknown. St. Athanasius speaks of 318. Most were Greeks; […] known Latins included Hosius of Cordova, Cecilian of Carthage, Mark of Calabria, Nicasius of Dijon, Donnus of Stridon, and Roman priests Victor and Vincentius. Famous members included St. Alexander, Eustathius, Macarius, Eusebius of Nicomedia, Eusebius of Caesarea, Nicholas of Myra, and the young deacon Athanasius.

The Council opened on 20 May 325; sessions began 14 June, the symbol was formulated 19 June, ending 25 August. Constantine, clad in gold, opened the session, expressing his will for religious peace. Theological discussions were directed by ecclesiastical leaders, chiefly Hosius, assisted by Victor and Vincentius. Arius was summoned and debated; most declared against his doctrines. St. Athanasius notes Constantine’s presence did not hamper the Council. The resulting Nicene Creed affirmed belief in one God the Father Almighty; one Lord Jesus Christ, begotten of the Father, consubstantial with the Father [homoousion to patri]; and in the Holy Ghost. It anathematized those claiming the Son was created or mutable. The adhesion was general; few opposed and were exiled. Arius’s writings were burned, and he was exiled.

Soon after Nicaea, new formulas of faith were composed, mostly variations of the Nicene Symbol, to meet new Arianism phases. […] The Nicene Symbol remained the standard among defenders of the Faith and gradually became the baptismal profession of faith. Its alteration into the Nicene-Constantinopolitan formula is usually ascribed to the Council of Constantinople (381), confirmed at Chalcedon (451) […] Some historians […] trace it to Epiphanius’ „Ancoratus“ (374) or St. Cyril of Jerusalem’s revisions. Others […] think it did not originate at Constantinople because Gregory Nazianzen mentions only the Nicene formula, and Latin Fathers knew nothing of it before the mid-fifth century.

The Constantinopolitan form […] enlarged the Nicene article on the Holy Ghost; several words, notably „of the substance of the Father“ and „God of God,“ are omitted; ten clauses are added; five passages relocated. […] Vossius (1577-1649) noted its similarity to Jerusalem’s baptismal formula. Whatever its origin, Chalcedon attributed it to Constantinople, adopting and authorizing it as a true expression of the Faith.